118 Life and Death, Heredity and Evolution 



although both sexes may be present in a single nucleus. But 

 individuals or cells in which the active material or kine- 

 toplasm prevails are male, while those in which the nutritive 

 material or trophoplasm is preponderant are female. 



According to such theories, for vigorous and successful 

 life, an organism must have both these substances or proper- 

 ties, both maleness and femaleness, in fitting proportions. 

 And it is the gradual dislocation of the required proportions 

 that gives rise to the necessity of periodical unions of di- 

 verse cells or nuclei, and to the rejuvenescence that results 

 from such unions. It is commonly held that as life goes on, 

 certain individuals or cells or parts of cells develop, perhaps 

 by accidental inequalities in division, farther and farther in 

 the direction of maleness, of activity, of energy-production ; 

 that is, the kinetoplasm exceeds greatly the trophoplasm. 

 Others develop farther and farther in the female or vegeta- 

 tive direction ; toward a decrease in activity ; toward a stor- 

 ing up of food and energy; toward a great preponderance 

 of trophoplasm. 



After this divergent development has gone on for a time, 

 in each case, according to such theories, a stage of too great 

 specialization is reached; a stage of lack of balance; the 

 male has developed too far in one direction, the female in 

 the other. Life can therefore no longer continue vigorously 

 and normally ; the chemical changes go awry ; the process 

 that we call aging comes on ; reproduction ceases ; and life 

 must end unless compensatory changes occur. Such com- 

 pensatory changes are brought about by a reunion of the 

 separated male and female substances or tendencies ; the 

 balance is thereupon restored. In other words, rejuvenes- 

 cence is produced by mating ; reproduction can now go on as 

 before ; the cycle of youthful life begins anew. 



According to this way of looking at the matter, there is 



